FBI Agent Rick DesLauriers said the two may have been involved in the bombings that killed three people and injured more than 170 people Monday.

"Somebody out there knows these individuals as friends, neighbors, co-workers, or family members of the suspect. Though it maybe difficult, the nation is counting on those with information to come forward and provide it to us," DesLaurier said.

One of the images shows a man in a dark hat. The other shows a man in a white hat. DesLauriers said the man in the white hat was shown on an image setting down a backpack at the site of the second explosion.

DesLauriers said the two appeared to be walking together through the crowd on Boylston Street in the vicinity of Gloucester Street.